The present invention relates, in general, to bleaching detergent compositions containing as a bleaching agent a peroxyacid compound, and as a bleaching stabilizer a defined hydroxycarboxylic polymer, and the application of such compositions to laundering operations. More particularly, the present invention relates to particulate bleaching detergent compositions which provide enhanced bleaching performance concomitant with a significant improvement in the stability of the peroxyacid bleaching species in the wash solution owing to the presence of said hydroxycarboxylic polymer.
Bleaching compositions which release active oxygen in the wash solution are extensively described in the prior art and commonly used in laundering operations. In general, such bleaching compositions contain peroxygen compounds, such as, perborates, percarbonates, perphosphates and the like which promote the bleaching activity by forming hydrogen peroxide in aqueous solution. A major drawback attendant to the use of such peroxygen compounds is that they are not optimally effective at the relatively low washing temperatures employed in most household washing machines in the United States, i.e., temperatures in the range of 80.degree. to 130.degree. F. By way of comparison, European wash temperatures are generally substantially higher extending over a range, typically, from 90.degree. to 200.degree. F. However, even in Europe and those other countries which generally presently employ near boiling washing temperatures, there is a trend towards lower temperature laundering.
In an effort to enhance the bleaching activity of peroxygen bleaches, the prior art has employed materials called activators in combination with the peroxygen compounds, such activators usually consisting of carboxylic acid derivatives. It is generally believed that the interaction of the peroxygen compound and the activator results in the formation of a peroxyacid which is a more active bleaching species than hydrogen peroxide at lower temperatures. Numerous compounds have been proposed in the art as activators for peroxygen bleaches among which are included carboxylic acid anhydrides such as those disclosed in U.S. Pat. Nos. 3,298,775; 3,338,839; and 3,532,634; carboxylic esters such as those disclosed in U.S. Pat. No. 2,995,905; N-acyl compounds such as those described in U.S. Pat. Nos. 3,912,648 and 3,919,102; cyanoamines such as described in U.S. Pat. No. 4,199,466; and acyl sulfoamides such as disclosed in U.S. Pat. No. 3,245,913.
The formation and stability of the peroxyacid bleaching species in bleach systems containing a peroxygen compound and an organic activator has been recognized as a problem in the prior art. U.S. Pat. No. 4,255,452 to Leigh, for example, specifically addresses itself to the problem of avoiding the reaction of peroxyacid with peroxygen compound to form what the patent characterizes as "useless products, viz. the corresponding carboxylic acid, molecular oxygen and water". The patent states that such side-reaction is "doubly deleterious since peracid and percompound . . . are destroyed simultaneously." The patentee thereafter describes certain polyphosphonic acid compounds as chelating agents which are said to inhibit the above-described peroxyacid-consuming side reaction and provide an improved bleaching effect. In contrast with the use of these chelating agents, the patentee states that other more commonly known chelating agents, such as, ethylene diamine tetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) are substantially ineffective and do not provide improved bleaching effects. Accordingly, a disadvantage of the bleaching compositions of the Leigh patent is that they necessarily preclude the use of conventional sequestrants, many of which are less expensive and more readily available than the disclosed polyphosphonic acid compounds.
The influence of sodium silicate, a common ingredient in commercial detergent formulations, on the decomposition of peroxyacid in the wash and/or bleaching solution is disclosed in copending applications Ser. Nos. 354,860 and 354,861, filed on Mar. 4, 1982. The undesired loss of the peroxyacid bleaching species in the wash solution by the reaction of peroxyacid with a peroxygen compound (or more specifically, hydrogen peroxide formed from such peroxygen compound) to form molecular oxygen is believed to be catalyzed by the presence of silicates in the wash solution. Conventional sequestrants are believed to be relatively ineffective in inhibiting the aforementioned silicate-catalyzed side reaction. Consequently, the compositions of the invention seek to provide a peroxyacid bleach species having substantially enhanced stability in the wash solution relative to that provided by conventional bleaching detergent compositions, particularly in the presence of silicates.
Hydroxycarboxylic polymers have been disclosed in the art as additives of laundry compositions, principally as sequestrants or builders in detergent compositions, or alternatively as materials which improve the shelf life of certain relatively unstable peroxygen compounds. Thus, for example, U.S. Pat. No. 3,920,570 describes a process for sequestering metal ions from aqueous solution using an alkali metal or ammonium salt of a poly-alpha-hydroxyacrylic acid as a replacement for sodium tripolyphosphate in the detergent composition. U.S. Pat. No. 4,329,244 discloses improving the storage stability of particles of alkali metal percarbonate or perphosphate by incorporating into such particles polylactones derived from defined alpha-hydroxyacylic acid polymers. However, the use of hydroxycarboxylic polymers for improving the stability of peroxyacid bleaching species in an aqueous wash solution has heretofore not been appreciated or disclosed.